This invention relates to multiple-beam radar systems, and more specifically to multiple-beam radar systems used in clear air wind profiling.
In various aeronautic and meteorological pursuits, it is sometimes desirable to profile the velocity and velocity gradient of air flowing through a predetermined volume or cell of the atmosphere. Measurements are typically taken a significant distance above a ground location by means of a Doppler radar capable of detecting the motion of air.
The basic geometry of remote wind profiling is shown in FIG. 1. The goal is to determine the wind velocity vector at a given point in space. Typically, this vector is inferred from direct and indirect measurements of velocity and velocity gradients obtained with radar beams directed in the vicinity of the point of interest. Two such beams, 20 and 30 directed to the North and East, respectively, by an array 10 of antenna elements are shown in FIG. 1. These beams are elevated with respect to the horizontal plane. Typically, array 10 may be a multielement parasitic array of linear (dipole type) elements. Such an array is commonly referred to as a Yagi-Uda or simply Yagi array, after its inventors. Specifically, array 10 is a square, regular array of such elements having each of its four corners pointed in the direction of respective points of the compass.
As is well known, the direction of a beam produced by an array is a function of the relative phase of the antenna elements. The two beams produced by an array such as that just described are thus produced alternately rather than simultaneously by altering the phase relation between the respective antenna elements in a known fashion.
It is also known to use an array such as that described to produce three beams, the third beam being vertical and used to measure directly a vertical component of wind velocity.
In theory it is possible, by appropriate phasing alternately to obtain any desired number of beams from an array such as that described. These beams could then be used to measure directly sufficient air velocity data that air velocity in the cell could be determined to any desired degree of precision. It must be appreciated, however, that using prior art techniques, the number of switches necessary and the concommitant complexity of such systems increase exponentially with the number of beams. Therefore, in prior art systems, there exists a tradeoff between the need and desire for more complete measurement of air velocity components versus a need to keep the cost and complexity of the system necessary to make those measurements as low as possible.